The prior art is replete with lubricant formulations useful in the rolling of metals such as aluminum.
With the evolution of rolling equipment toward rolling mills that produce higher pressures at ever-increasing operating speeds, the demands placed on the lubricants used in such mills have increased with each new generation of rolling equipment. Such increasing demands have resulted in further expansion of the list of lubricant formulations useful in rolling operations.
To the best of our knowledge, however, there are certain attributes which a metal working lubricant must possess to be a suitable material for cold working of metal, such as cold rolling of metal foil or sheet or foil-plastics film laminates, stamping, drawing and ironing. These attributes include the ability to (1) withstand the high shear forces encountered during metal working, (2) provide a highly specular surface, (3) exhibit extreme pressure lubricating properties, (4) operate as a single phase lubricant, (5) provide good heat transfer, (6) provide a clean, streak-free surface upon subsequent heat treatment, and (7) prevent transfer of metal oxides from the workpiece to the tool.
Each of these characteristics is familiar to the skilled lubricant technician. Most of the above-stated attributes are self-explanatory. Some of these, however, need further explanation.
The ability to provide adequate extreme pressure lubrication defines the ability of the lubricant to reduce or prevent conditions of seizure or welding between the tool, e.g., the rolling mill, etc., and the workpiece under conditions of extreme load.
The ability to operate as a single phase lubricant provides uniform fluid film in the tool-workpiece interface. It also permits the lubricant to undergo reclamation processes, such as filtration, centrifugation, etc.
The term single phase lubricant refers to a lubricant in which the components of the lubricant are soluble at room temperature. This is in contrast to macroemulsion lubricants, sometimes incorrectly referred to as "soluble oil" lubricants, and microemulsion lubricants, which have dispersed phase droplets predominately less than 0.2 micrometers in diameter.
Thus, it has been the aim of the formulators of lubricants to design a formulation which provides all of the foregoing properties.
However, most known lubricants which exhibit all of the desired properties have problems of their own. These problems include (1) fire hazard, (2) toxicity hazard, (3) unacceptable air emissions, (4) cost, and (5) poor productivity. These problems result from the fact that these lubricants are petroleum based.
It is also known from U.S. Pat. No. 4,636,321 to provide an aqueous lubricant which overcomes the problems associated with petroleum based lubricants. However, the compositions of this patent are relatively complex. When using these compositions, it is necessary to constantly monitor the working fluid to maintain the proper ratio of ingredients and replenish depleted components. Thus, it is a primary purpose of the present invention to provide an aqueous metal working lubricant of simplified composition, thereby permitting ease of maintenance of the working fluid while maintaining or improving all of the desirable lubricant properties of the known compositions.